Evaporative humidifiers typically include an airflow plenum housing, a water reservoir, a blower for producing a positive pressure flow of air through the plenum housing, and an evaporative core coupled to the reservoir for imparting moisture to air flowing through the housing. The evaporative core is maintained in a moist state by means of a water supply system which circulates water from the reservoir to evaporative media within the core, with water trickling through the core for evaporation into the air flowing through the evaporative media. The evaporation rate, and therefore the humidification performance of the apparatus, is directly related to the rate of air flow through the evaporative core.
Bypass dampers have been successfully used in the past for capacity control of evaporative humidifiers. A limitation on the operation of conventional variable capacity humidifiers, however, has been that the flow exiting the humidifier station is stratified. That is, the portion of the airstream output from the evaporative core is cooler and more humid than the bypass portion of the airstream flowing through the bypass damper, which may be at ambient temperature and humidity, or preheated to an elevated temperature and reduced humidity level for control purposes.
Another limitation of conventional humidifiers relates to reliability and maintenance requirements. Conventional multistage humidifiers include evaporative media having a thickness of approximately six inches. It is not uncommon for conventional evaporative media core structures to catastrophically fail by twisting, bowing or collapsing.
Accordingly, there presently exists a need for a variable capacity evaporative humidifier which avoids the problem of stratification inherent in the operation of a conventional bypass damper configuration. In addition, an evaporative humidifier configured to reduce the media failure problems experienced in the past is needed.